* Zipproxy - http://ziproxy.sourceforgehttp://ziproxy.sourceforge.net/.net/ is a related application, but does not implement the core of this proposal, which is compressing webpages based on the known contents of the users cache.

* Zipproxy - http://ziproxy.sourceforgehttp://ziproxy.sourceforge.net/.net/ is a related application, but does not implement the core of this proposal, which is compressing webpages based on the known contents of the users cache.

Latest revision as of 13:31, 21 July 2009

Wishes warning! This article or section documents one or more OpenMoko Wish List items, the features described here may or may not be implemented in the future.

This is an outline of a proxy to reduces data transfer - for use on devices with a reasonable amount of persistant storage, and very limited bandwidth.

Some aspects could later be included in browsers or webservers.

Once, each page linked to a subpage of contents, which remained static, and could be easily refreshed if it changed based on dates in the HTTP headers.

Now, this is the case in the minority of popular sites.

Most sites now have a substantial fraction of pages with some non-static contents.

(Zipproxy, is an example of software implementing this type of compression.)

A very simple test, using diff and gzip however, revealed that the variation between pages is quite small.

This means that if the user clicks 'reload', if the proxy simply compresses the page, the user needs to download 15K.

If, however, the user-agent and the proxy act in concert, this can be reduced to under 0.5K. (split on "<", count the compressed differences).

This is done by the user-agent caching the pages it downloads, then informing the proxy of which version of the page it has.

The proxy then simply sends the compressed differences between the previous and current version.

Other optimisations.

Comparing pages, and ensuring that any page has in fact changed before downloading, as many servers misreport pages changed when they have not.

Convert all jpegs to progressive, and initially only download the first 'scan' of the image, which is 1/8th the size or so. Allow the user to download the remainder of the file for full resolution by clicking on it.

If the proxy knows the exact state of the clients cache - for example if it's the only proxy the client uses - it does not need to negotiate it with the client, it can simply send only the compressed differences.

If the user visits a new page on a site - the proxy can compare the hashes of parts of the newly downloaded page, with others the client has cached, and instead of sending the whole file, send only the (compressed) differences.

For example - ebay - auction pages share a large amount of common text - all the in-page javascript, footers, headers, and navigation bar.

The proxy can automatically download and include required elements if the user wishes them - for example automatically including images and javascript, without another round-trip to the server.

Converting images to lower resolution forms. For example - convert all jpegs to progressive jpeg, and serve up only the first 1/8th of a file.

(Zipproxy, is an example of software implementing this type of compression.)

A very simple test, using diff and gzip however, revealed that the variation between pages is quite small.

This means that if the user clicks 'reload', if the proxy simply compresses the page, the user needs to download 15K.

If, however, the user-agent and the proxy act in concert, this can be reduced to under 0.5K. (split on "<", count the compressed differences).

This is done by the user-agent caching the pages it downloads, then informing the proxy of which version of the page it has.

The proxy then simply sends the compressed differences between the previous and current version.

Other optimisations.

Comparing pages, and ensuring that any page has in fact changed before downloading, as many servers misreport pages changed when they have not.

Convert all jpegs to progressive, and initially only download the first 'scan' of the image, which is 1/8th the size or so. Allow the user to download the remainder of the file for full resolution by clicking on it.

If the proxy knows the exact state of the clients cache - for example if it's the only proxy the client uses - it does not need to negotiate it with the client, it can simply send only the compressed differences.

If the user visits a new page on a site - the proxy can compare the hashes of parts of the newly downloaded page, with others the client has cached, and instead of sending the whole file, send only the (compressed) differences.

For example - ebay - auction pages share a large amount of common text - all the in-page javascript, footers, headers, and navigation bar.

The proxy can automatically download and include required elements if the user wishes them - for example automatically including images and javascript, without another round-trip to the server.

Converting images to lower resolution forms. For example - convert all jpegs to progressive jpeg, and serve up only the first 1/8th of a file.